Field of Invention
The present invention relates to a field of detection technique, and in particular to a method for detecting a defect of a pipe, a device for detecting the defect of the pipe and an apparatus for detecting the defect of the pipe.
Description of Related Arts
With advances in science and technology and requirements in industrial production, a range of usage of a transporting pipe becomes increasingly broad. A long distance transporting pipe is a main transporting manner of a production in an industry of petroleum natural gas. And, if the long distance transporting pipe for the petroleum natural gas has a malfunction such as a leakage or the like, it causes pollution in addition to losses of shutdown and salvage. Therefore, how to ensure a safe operation of the existing long distance transporting pipe and new pipe for the petroleum natural gas to reduce a probability of a security accident and implement a intrinsic safety of the operation of the pipe is an urgent affair of ensuring the safe operation of the pipe.
Since the long distance transporting pipe for the petroleum natural gas is buried underground generally, a main working flow of detecting a defect of such buried pipe are still the following steps: excavating, stripping an antisepsis (incubation) layer, detecting, enclosing and backfilling. It is obvious that this is a destructive detecting method, and a representativeness of data detected and a reliability of an evaluating conclusion are affected by numbers of points excavated (sampled) and a distribution range thereof. Therefore, how to detect the buried pipe without excavating and stopping transporting is a problem that deserves an in-depth exploration.
There are many conventional methods of nondestructive detecting including a method of ultrasonic detection, a method of vortices detection and a method of ray detection. The ultrasonic detection is implemented by using information provided by an interaction between an ultrasonic wave and an object, and the ultrasonic wave can propagate in a metal. an deficiency of such method is that an attenuation of the ultrasonic wave in the air is fast, and there needs a propagation medium of the ultrasonic wave, which may be a coupling agent such as oil or water generally at the time of detection, so it is not appropriate for detection of the buried pipe.
The method of ray detection is a method of nondestructive detecting by using a physical effect (for example, a variation of intensity of radiation, scattering or the like) generated by an interaction between ionizing radiation and a subject to detect a discontinuity, a structure or a thickness or the like in a work piece. It is also not appropriate for the detection of the buried pipe.
The method of vortices detection operates according to a principle of electromagnetic induction, so the method of vortices detection can detect a surface defect and a near surface defect of the work piece. A notable feature of the method of vortices detection is functioning to electrically conductive material rather than ferromagnetic material, but an effect of the ferromagnetic material is not good. Secondly, a fineness, a smoothness, a border or the like of the surface of the work piece to be detected has large influence to the vortices, thus, the method of vortices detection is usually used to the detection of non-ferromagnetic work piece such as a copper tube or the like which has relatively regular shape and relatively clean surface. If the buried pipe is a ferromagnetic pipe, the method of vortices detection can't be used. And, the method of vortices detection also needs an exciting source, and it still needs excavating to detect the buried pipe.
A Chinese patent CN102095080A disclosed a method for detecting the buried pipe using a magnetic method without excavating, and its principle is using magnetism that the buried pipe magnetized by an earth magnetic field itself has as the exciting source and using a flux gate sensor having 1 nT of a resolution of magnetic induction intensity to detect the magnetic induction intensity and attenuation amount above a lower side, and continuing detection results downward at the same time, and detecting a quality of the pipe by data processing. However, it does not disclose how to detect the defect of the buried pipe specifically in the disclosure, thus, it can't determine a position of the defect and a magnitude of the defect of the buried pipe.